Event dialog: fix content editor and attendees dialog

As window menu and toolbar belong to the parent, the inner iframe can't
modify them.

from parent using the receiveMessage() function.

Now that the main dialog is included in an iframe, we have to communicate
with the iframe from the parent to give to the iframe the good commands.

The structure of sendMessage/receiveMessage come from the Lightning project.
Especially the sendMessage() function which send command with the good event id
(needed for tab view).

Tabs have been replaced by spaces too as most of the file where replaced
too.

To reflect clearly the calendar event dialog has been moved to an iframe
by Lightning, we move all our stuff to the new name.

Fix javascript code to:
 * avoid removing event listener
 * avoid using try/catch without need
 * avoid to reset current set of items, but instead add back attachment
   if not already in toolbar and url attachment is there

This is to be sure to be called after the Lightening onLoad() listener.

This reverts commit 9f0aacb7.

I'm reverting this change, since I use now correctly formatted xhtml which avoids exceptions while saving content to innerHTML.

correctly setup current window.

to get valid xhtml code (with XML tags well terminated)

This code was the same than the original Lightening code contained in
chrome://messenger/content/messenger.xul

Exchangecalendar has nothing added and the overlay is bugged:
 * it didn't overlay the context menu in the attendee tab on the
bottom of the dialog
 * it didn't display days and times in the header of attendee dialog

This commit fix the overlay, but the JavaScript needs now fixes
to hide/display exchangecalendar items with the good context.

Fix meeting response proposed start and end time by @jaroslawp

Fix code style changes and code cleanup by @Trim

Now, our editAttendees dialog show up, but isn't full working